Dead Studer A730

[lumanauw]

I've got a friend who has a dead Studer A730. I'm not familiar with digital, but is it possible to fix this CD player? What to check first?

 

[MadMutt]

Define dead.

Had a 225 (?) revox here that wouldn't power up.
Was some shorted electrolytic caps on the power board.
Had blown the fuse because of this.

 

[lumanauw]

Nothing happens when the ON knob is pushed. All the displays are dead, nothing happens when any of the buttons are pushed on.

 

[jives11]

check for fuses

at the risk of suggesting the obvious, is there an internal fuse ? I have an old Philips 104 and the Power supply has a fuse on the circuit board , accessible only from underneath, having removed the lower plate.

 

[MadMutt]

I can garantee theres a fuse (or more) inside the unit.
Pics I've seen of the 731 version would suggest that they also have a fuse IN the power socket on the rear panel.

That'd be my first check.

 

[georgehifi]

I've got a friend who has a dead Studer A730. I'm not familiar with digital, but is it possible to fix this CD player? What to check first?

If you can use it lumanauw,
ftp://ftp.studer.ch/Public/Products/CD/A730/Manuals/

Cheers George

 

[lumanauw]

Hi, Everybody,

Thanks for the inputs 😀

Thanks, Georgehifi. That is one big file, 59Mb 😀

From quick check, all the fuses are OK (2 fuses are inside the AC plug-in, 4 fuses inside the unit).
I found something strange. The voltages at opamp rails are not symmetrical, +11Vdc (pin8) and -14Vdc (pin4).

 

[lumanauw]

Hi, Everybody,

I've looked more closely through the dead StuderA730.
-From outside panel (keyboard) not 1 single LED is on. All LEDs and 7segments are off, no matter what button I push, nothing happens.
-If I put a CD inside the tray, the CD spins, but no LED or 7segments is on. All indicators are dead.
-All the fuses are OK, the DC voltages from power supply are all present and normal. 2 LEDs are illuminating inside the unit, one red LED and 1 green LED on the right-down corner.
-The power supply heatsink (a piece of aluminum sheet) is a bit hot.
-There's an IC with code SAA7220 (position near TP5-TP6) is very hot. Is this normal? From the datasheet it is a digital filter IC.

Here's voltage measurement on Test Points (TP) as I measured them VS as written in the service manual.
I measure the voltage in dead condition, the service manual said the voltages are in "play mode", so could be different.

Anyone can help to interprete what is going on?

 

[stephensank]

You probably have one or more power supply filter caps going bad. If you measure more than 10mV or so of AC voltage on the regulated DC supply lines(like the points where you got 11 + 14v), then look for the big lytic caps before the supply regulators to be bad.

 

[MadMutt]

I'd also go the re-cap route.
It's what stopped the one (226 vintage) I had here.

Although the display issue may not be affected by this.